BY PAUL JACOBSON, SENIOR TECHNICAL LEADER, EPRI
In December 2011, the Electric Power Research Institute (EPRI) completed an assessment of the US ocean wave energy resources with the Virginia Tech Advanced Research Institute and the National Renewable Energy Laboratory (NREL). The team developed methodologies for estimating the naturally available and technically recoverable resource using a 51-month hindcast database developed specifically for the assessment by the National Oceanic and Atmospheric Administration’s National Centers for Environmental Prediction.
The project team encountered a wide variety of interpretations of wave energy resource terminology among peer reviews of the assessment, and an outside Marine and Hydrokinetic Energy Technology Assessment Committee, facilitated by the National Research Council with funding support from the U.S. Department of Energy.
EPRI adopted the globally used “wave power density” metric in terms of kilowatts per meter (kW/m) of a unit diameter circle to aggregate the total available wave energy resource for a given nation or coastal region. The average annual and 12 monthly available wave power densities were estimated at more than 42,000 grid points in a U.S. coastal four-minute grid, mapped out to a distance of 50 nautical miles from shore, which coincides with the limit to which NREL mapped the offshore wind power density.
The total available wave energy resource along the U.S. continental shelf edge is estimated to be 2,640 terawatt-hours per year (TWh/yr). The table compares these results with a preliminary estimate made by EPRI during its offshore wave energy conversion feasibility study in 2004.
Increases in the 2011 assessment from 2004 results are largely because the prior estimate was intentionally conservative, based on a survey of selected National Data Buoy Center buoy measurements, which was representative but did not cover the full range of coastal exposures and sheltering by shoreline features and islands. The increase is markedly greater for the East Coast than the West Coast and Alaska because the 2004 estimate was rounded to the nearest 5 kW/m, which has a much greater effect for the lower wave power densities of the East Coast.
The total recoverable wave energy resource, as constrained by an assumed array capacity packing density of 15 MW/km of coastline, with a 100-fold operating range between threshold and maximum operating conditions in terms of input wave power density available to such arrays, yields a total technically recoverable resource along the U.S. continental shelf edge of 1,170 TWh/yr, comprising 250 TWh/yr for the West Coast, 160 TWh/yr for the East Coast, 60 TWh/yr for the Gulf of Mexico, 620 TWh/yr for Alaska, 80 TWh/yr for Hawaii, and 20 TWh/yr for Puerto Rico.
To put these estimates into context, annual U.S. electricity consumption is about 4 trillion kWh/yr and the assessment’s total U.S. wave energy potential equals 2.6 trillion kWh/yr. The available U.S. wave energy corresponds to roughly half of U.S. electricity consumption. However, the estimated technically recoverable wave resource is about 1.1 trillion kWh/yr, or about one quarter of U.S. electricity consumption.
EPRI’s wave energy assessment report “Mapping and Assessment of the United States Ocean Wave Energy Resource” is available for download at http://epri.co/1024637.